Prostate cancer is the most frequent non-skin cancer, the second leading cause of cancer death in U.S. men, and is increasing in incidence. Effective prevention requires a better understanding of the etiology of prostate cancer, a major goal of this P01's biological studies of the historical Prostate Cancer Prevention Trial (PCPT). A randomized, controlled trial of finasteride in 18,882 men, the PCPT found a 24.8% decrease in overall prostate cancer risk and an apparently increased risk of high-grade disease (New England Journal of Medicine [NEJM], July 2003). Prostate cancer is an androgen-dependent disease, and finasteride inhibits 5a-reductase, thus blocking the conversion of testosterone (by 5a-reductase) to dihydrotestosterone, the most active prostate androgen. The five proposed highly interactive P01 studies of the PCPT are: Project 1, Androgen Metabolism;Project 2, Diet and Diet-Related Factors;Project 3, Insulin-like Growth Factor Axis and Insulin Resistance;Project 4, Genotypic and Phenotypic Studies of Inflammation;and Project 5, Oxidative Damage and DNA Repair. These projects will use nested case (n=1800)-control (n=1800) designs to develop the P01 theme, which is the genetic, metabolic and environmental factors associated with the risk of prostate cancer overall or high-grade disease and the effects of these factors on finasteride preventive efficacy. The mechanisms underlying these risk-factor associations also will be assessed. Major elements of the P01 theme are the study (1) of genetic polymorphisms to identify molecular prostate cancer risk factors and determine pharmacogenetic profiles and (2) of somatic mutations to discover the mechanisms underlying increased high-grade prostate cancer risk associated with finasteride. The P01 provides each project access to the invaluable repository of PCPT biospecimens and data. Each project is closely linked by interactive specific aims and planned collaborations with the other 4 projects and 3 cores. Unique P01 strengths include its biopsy-confirmed control group, the value of which is underscored by PCPT data indicating a substantial prevalence of cancer and high-grade disease in men with "normal" prostate-specific antigen and digital rectal exam (NEJM, May 2004), and standard centralized histological classifications. With fully clarified interactions and a large amount of highly relevant new preliminary data, this resubmitted P01 promises to develop comprehensive prostate cancer risk models important to the future study and prevention of prostate cancer.